US2429792A - Magnetic recording-reproducing means and system - Google Patents

Description

0t. 2s,- 1947. BEGUM 2,429,792

MAGNETIC REOORDING-REPRODUCING MEANS AND SYSTEM Filed April 7, 1943 u N6 AMPLIFIER IN V EN TOR.

FUR/Vi).

Patented Oct. 28, 1947 MAGNETIC RECORDING-REPRODUCING .MEANS SYSTEM Semi Joseph Begun, Cleveland Heights, Ohio, as-

signor to The Brush Development Company, Cleveland, Ohio, a corporation of Ohio Application April 7, 1943, Serial No. 482,198

17 Claims. ((31. 179-1002) My invention pertains to magnetic record transducing, and more particularly to the record-' ing, reproducing, and obliterating heads which are used with magnetic systems, and is a continuation in part of my application Serial Number 6 399,909, filed June 26, 1941, now abandoned.

An object of my invention is to provide means for mre-effectively demagnetizing a magnetic material.

Another object of my invention is to prevent signal interference between magnetic demagnetizing means and magnetic recording and reproducing means.

A further object of my invention is to provide new and improved recording and/ or reproducin heads.

Other objects and a fuller understanding of my invention will be had by referring to the following description and claims, taken'in conjunction with the drawing in which:

Figure 1 represents one form of demagnetizing or obliterating head utilizing an air core coil.

Figure 2 illustrates another form of demagnetizing or obliterating head utilizing an iron core coil.

Figure 3 illustrates another form of obliterating head utilizing an iron core of a different shape.

Figure-4 illustrates an air core coil obliterating head with a different electrical connection, and

Figure 5 illustrates my new recording and re- '30 producing heads and their positions with respect to'my new obliterating head to form a new magnetic recording, reproducing, and obliterating system.

Figure 1 illustrates diagrammatically the portion of a magnetic recording'and reproducing system whichis usedto obliterate or demagnetize the magnetic material prior to the recording of a signal. If the previously recorded signal is not obliterated before a new record is put on the 40 tape, mixed records are apt to result. This oblitration may be obtained by applying a magnetizing force to the tape which is sufilciently high in value to cause an induction which saturates the magnetic material. It may also be obtained 4 by applying over a relatively large area of the magnetic material an alternating magnetizing force, and gradually reducing the magnetizing force to zero to reduce the residual magnetism in the magnetic material to substantially zero.

This I do by moving the magnetic material, such as the magnetic tape 2|, past an obliterating head which is establishing a diffuse alternating magnetic field. The decrease in strength of the magnetizing force is obtained for each portion of 65 5 diffuse.

the tape by removing that portion of the tape farther and farther from the center of the ma netic field which is established by thecoils 22,23 andthe alternating current generator 24. Continuous alternating current is applied to the air core coils 22, 23 which in this case form the obliterating head, and which are positioned near the magnetic tape 2!. This.causes'a rapidly reversing diffuse magnetic flux to be impressed through a large areaof the tape, and as each incremental portion of the tape moves farther and farther away from the center of the field the strength of the field on that portion of the tape decreases until it' is effectively zero. The field is alternating as it is established by-an alternating current in the coils 22, 23 and the frequency of alternation should be high enough that at the particular rate of speed of movement of the tape each incremental portion of the tape is subjected to several reversals of polarity of the flux field before it moves sufficiently far away from the field so that the field has no'efiect. The coils 22 and 23 should be wound in opposite directions in order that the fiux field established by them is The field should be broad enough that each incrementa1 portion of the tape remains in it for a length of time suflicient to cause it to undergo several reversals of polarity. This broad field is established by the coils 22, 23 being wound in opposite directions to cause the polarity of the magnetic field established by one coil to be such that it bucks the magnetic field established by the other coil. At any one instant two north magnetic poles will face each other through the tape 2|, and at the next instant, due to the reversal of polarity occasioned by the alternating current in coils 22, 23, there will be two south magnetic poles facing each other through the tape.

Figure 2 illustrates a form of my invention in which the air cores of coils 22, 23 are replaced with iron cores 26, 21. Different shaped iron cores may be'used and the coils may be wound about the cores in different ways and still come within the scope of my invention.

An example is shown in Figure 3 in which an iron core coil is wound in one direction and one leg of a U-shaped iron core 28 is wound in the same direction. The U-shaped core is positioned with respect to the tape 2| and the core 26 so that the core 26 is opposite the leg which is not wound and the tape is between the unwound leg and the core 26. With this arrangement the two coils are wound in the same direction but a bucking fiux will be established through the tape 2 I.

bucking magnetic flux.

Figure 4 illustrates an obliterating head having air cores and in which the coils 22. 23 are wound, in the same direction, but which still establish Although I have shown .the axes of the coils and cores running the width of the tape, it is head-indicated generally by the reference character 3|. Illustrated is the head shown in Figure 2, but any other obliterating head which establishes a diffuse alternating field could be used.

The tape 2 I is adapted to move in the direction of arrow 33, and after passing the obliterating head, which for convenience is indicated generally by the reference character 29, it passes the recording head 30, and then the reproducing or pick-up head 3|. The recording head 30 comprises two pole pieces 40, 4|, about which are wound two coils 42, 43, and the coils are connected to a source 44 of alternating or unidirectional signal current. The coils 42, 43 are wound in the same direction to cause aiding magnetic fiux fields to be set up through the tape 2 I, there.-;

by establishing a focused or narrow fiuxfield between the two pole pieces 40, 4|. Each incremental portion of the tape 2| .quickly moves out of the influence of the focused magnetic field to prevent substantial demagnetism due to the alternating character of the signal to be recorded, and thereby leaving on the tape 2| a magnetic condition which can be reproduced. The pole piece 4| is ofiset slightly in the direction of movement of the tape 2| to cause the magnetic flux to travel longitudinally through the tape for a short distance. This is known as the longitudinal method of magnetic recording. My obliterating head and my system can also be used with the well known perpendicular method of magnetic recording and reproducing.

After a signal has been magnetically recorded on the tape 2|, the tape passes under the reproducing head 3| which is comprised of a pole piece 50 and a coil 5|, and an electromotive force is established which is amplified by the amplifier 52, and is then used to actuate a utilizing device 53. The utilizing device maybe a loud-speaker, oscillograph, pen recorder, or any other such device.

' Due to the broad diffuse nature of the alternat-- ingmagnetic field established by the obliterating head 29, there is apt to be signal interference with the recording head and with the pickup head 3| unless special precautions are taken. One precaution, which is effective if properly applied but which increases the cost of any device, is magnetic and electrostatic shielding. In many cases, due to space and weight limitations, shielding cannot be used. I reduce interference between the obliterating signal and the recording and re-. producing signals by orienting the axis of the magnetic field established by the obliterating head 29 so that it is at substantially a 90 degree angle to the axis of the recording head 30, and at substantially a 90 degree angle to the axis of the reproducing head 3|. This establishes a magnetic recording, reproducing, and obliterating system with a minimum of cross-talk and hum, without the use of heavy and cumbersome shielding.

For many applications of magnetic recording, and reproducing systems very high frequencies are desirable. Several methods of obtaining these high frequencies are possible, and one of them is to-increase the speed of movement of the magnetic tape with respect to the pole pieces. This, of course, increases vibration and increases wear on both the tape and the pole pieces. One objection to the high tape speed has been that the sideways movement of the tape with respect to the pole pieces has increased-to the extent that unless the recording pole pieces are wider than the magnetic tape 2| the full width of the tape will not have a signal recorded on it, and, consequently, when that portion of the tape moves under the reproducing pole piece the electromotive force generated in the head will be less than it should be. Even if the signal had been recorded on the full width or the tape, side sway of the tape with respect to the reproducing pole piece would result in reduced amplitude of the reproduced signal. To obviate this undesirable result I make the pole pieces of the recording and reproducing heads wider than the magnetic tape 2| by an amount equal to or greater than the extent of the sideways motion of the tape in order that the minor sideways motion of the moving tape will have substantially no effect on the amount of flux passing between the tape and the pole pieces as the full width of the tape is always in contact with the pole piece. To forcefully restrain the tape and thereby substantially prevent the sideways motion would materially increase the wear on the tape, and, it the tape had a joint, might "be very impractical due to the slight extra thickness and width which the joint might have. These pole pieces of increased widthmay also be used with a magnetic recording and reproducing system which utilizes the well known perpendicular method ofmagnetization.

The expression magnetic record transducing" as used herein in the specification and claims is intended to mean either the operation of magnetically recording signals on a magnetic recording medium, or the operation of reproducing magnetically recorded signals, or any combination of these operations.

Although I have described my invention with a certain degree of particularity, it is to be understood that other arrangements can be made which come within the scope of my invention.

I claim as my invention:

1. In a telegraphone utilizing a moving record member, a source of alternating current, erasing means connected to said source and having two portions the first of which is positioned on one side of said record member and the second of which is positioned on the other side of said rec- 0rd member substantially opposite said first erasing portion, said erasing means comprising coil means so wound as to establish in said record member two magnetic iiux fields which oppose each other to form a broad diffuse magnetic fiux field and a stray flux field in the air around said erasing'means, and transducer means for magnetically transducing records on said record member and including pole piece means in fiux linkage relationship with said record member, said transducer means being located sufficiently close to said erasing means that it is within the said stray flux field, the direction of the fiux field in said transducer means being at an angle of substantially degrees to the direction of the said two opposing fiux fields produced by said erasing means whereby the influence of -the said stray flux field on said transducer means is minimized.

ing north and south magnetic poles and positioned on one side of said record member, second erasing pole piece means connected to said source member, alternating current erasing pole piece means having a first coreand a second core D sitioned on opposite sides of said record member, a first coil about said first core, and a second coil about said second core, said first and second coils bein adapted to carry said alternating current to establish said cores as first and second magnets, the direction in which said coils are wound about said cores being such as to cause the flux established by the first of said magnets to be in opposition to the fiux established by the second of said magnets to establish a diffuse magnetic field through which said moving record member moves, alternatin current recording means having pole piece means extending in a direction substantially perpendicular to the record member and perpendicular to the direction between said two magnets, recording coil means about said recording core means and adapted to carry alternating signal current to establish a narrow magnetic field through which said record member moves.

4. In a telegraphone, a moving record'member, magnetic obliteratin means having first coil means on one side of said record member and second coil means on the opposite side of said member and wound in a direction to establish magnetic fiux which bucks the flux established by said first coil to establish a diffuse magnetic field through which said record member moves, and transducer means having pole piece means associated with said record member for magnetically transducing records on said record member, the direction of the axis of said opposing coil means and the direction of said pole piece means being at a substantially 90 degree angle to substantially eliminate interference between said diffuse magnetic field and the magnetic field in said transducer means.

5. An obliterating head for a telegraphone having a, magnetizable material which is adapted to move, comprising in combination, a source of alternating current, means connected to said source of alternating current for establishing a first alternating magnetic fiux field, and means connected to said source of alternatingcurrent for establishing a second alternating magnetic flux field, said first and said second means being positioned with respect to each other and to said magnetizable material to establish flux fields in said material which tend to oppose each other thereby establishing a broad diffuse fiux field.

6. An obliterating head as set forth in claim in which themeans for establishing the first alternating fiux field and themeans for establishing the second alternating fiux field include a common source of alternating electrical signal.

7. An obliterating head for a telegraphone 6 having a magnetizable material which is adapted to move, comprising, in combination, means positioned on one side of said magnetizable material for establishing a first magnetic flux field through said magnetizable material, means positioned on another side of said magnetizable material and Opposite said first means for establishing a second magnetizable fiux field through said ma netic material which tends to oppose said first magnetic fiux field to cause the resultant fiux' 8. An obliterating head as set forth in claim '7 in which the resultant magnetic fiux field saturates each incremental portion of the magnetic material which is within the full effect of the field, and in which the magnetic field alternates with a frequency such that approximately ten alternations will take place between the time an incremental portion of the magnetic material is saturated and the time the incremental portion moves out of range of substantial magnetic eiTect from said means for establishing said magnetic fiux.- a

9. An obliterating head for a telegraphone having a magnetizable member comprising, in combination, first coil means positioned on one side of said magnetizable member, second coil means positioned on another side of said magnetizable member, and alternating signal source means connected to said first and said second coil means, said coil means being wound, oriented, and connected to said signal source in a manner to cause like magnetic poles to be established which tend to oppose each other at all times whereby a broad diffuse alternating magnetic field is established through the said magnetizable member,

10. An obliterating head for magnetizable material comprising in combination; first magnetic flux producing means positioned to one sidev of alternating bucking magnetizable'fiux fields are produced through said magnetic material.

11. In a telegraphone utilizing a magnetizable record member, a source of alternating current, first and second coil means connected to said source of alternating current and positioned in magnetic fiux linkage relationship with said record member, said coil means being so wound and oriented with respect to each other that at least two magnetic flux fields which tend to oppose each other are established in said record member.

12. In a telegraphone utilizing a magnetizable record member, a source of alternating current, coil means connected to said source of alternating current, core means associated with said coil means, said core means being so positioned with rent and associated with said record member for establishing two alternating fiux fields which saturate the record member and tend to oppose each approximately ten alternations take place in an incremental portion of the magnetizable material as the incremental portion moves from the point of magnetic saturation to a point out of range of substantial magnetic efiect from said means for establishing said magnetic flux.

14. In a telegraphone utilizing a moving magnetizable record member, a source of alternating current, coil means connected to said source of alternating current for establishing two alterhating magnetic flux fields, said coil means being so positioned with respect to said magnetizable record member that said two flux fields tend to oppose each other whereby a diffuse alternating flux field is established in said record member for demagnetizing said record member.

4 15. The method of conditioning a magnetizable record member for a telegraphone which comprises the steps of: establishing a first alternating magnetic flux field, establishing a second alternating magnetic flux field which tends to oppose said first fiux field whereby a diffuse alternating fiux field is established, and moving said record member through said diffuse alternating flux field at a rate of speed so related to the frequency of alternation of said diffuse fiux field that not less than about ten alternations take place in an incremental portion of the record member as the incremental portion moves from the point of maximum magnetic flux concentration to a point out of range of substantial magnetic effect of said diffuse field.

16. The method of conditioning a magnetizable record member which comprises the steps of: establishing a first alternating magnetic flux field, establishing a second alternating magnetic flux field which opposes said first flux field whereby a diffuse alternating fiux field is established of a value such that it substantially saturates the record member, and moving said record member through said difiuse alternating flux field at a ratev of speed so related to the frequency of alternation of said diffuse fiux field that as each incremental portion of said record member moves from the point of magnetic saturation to a point out of range of substantial magnetic effect of said diffuse field the said incremental portion is subjected to a sufficient number of reversals of the direction of the magnetic field that substantially no residual magnetism remains in the record member.

1'7. In a telegraphone utilizing a record member moving at a given rate and having recordingreproducing means in magnetic fiux linking relationship with said record member for recording and reproducing signals within a given frequency range, record member obliterating means comprising first means for establishing a first alternating fiux field in said record member and second means for establishing a second alternating flux field in said record member, said first and second alternating flux fields being so located with respect to each other and establishing fields of the same polarity to cause the fields within the record member to be diffused, and the frequency of alternation of said obliterating fields being within the frequency range of the signals recorded and reproduced while said record member is moving at said given rate.

SEMI JOSEPH BEGUN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,281,793 Patrick May 5, 1942 2,272,821 Roys Feb, 10, 1942 2,265,831 Wooldridge Dec. 9, 1941 2,306,162 Gipe Dec, 22, 1942 1,815,010 Pollock July 14, 1931 1,459,202 Fuller June 19, 1923 FOREIGN PATENTS Number Country Date 591,368 Germany 1929

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